Currently, an increase in system scale and a phenomenon where a field that has not been systematized is suddenly turned into a large-scale system are in progress in various fields. A typical example of the former is found in the IT field such as data centers and networks that are related to a technology called cloud, and the scale thereof is increasing year after year. An example of the latter is found in the infrastructure field such as electric power, energy networks, and cities, which are suddenly becoming targets to be controlled as a smart grid, a smart city, or other large-scale system cases. How large-scale systems are to be controlled is therefore expected to be a very important issue in the near future.
Add to that, the energy-conscious mindset of today's society demands control that does not waste electric power by shutting down an idling machine or the like. This is a trend not exclusive to the IT field and the infrastructure field. A generally effective action is, for example, exerting control so as to shut down a control object that is idling.
In the case of electric power grids, though only a limited number of electric power houses are controlled in this manner at present, an issue of which power house is to be activated and which power house is to be shut down for efficient generation of electricity has been studied for a long time. This is a matter of load balancing, and is hereinafter referred to as “unit commitment problem”. The unit commitment problem includes not only the issue of which power house is to be activated/shut down but also an issue of allocating load optimally among active power houses after determining for each power house whether to activate or shut down. This is a comprehensive matter of activation/shutdown and optimal allocation of load. In the following, the “unit commitment problem” as used herein includes both the issue of activation and shutdown and the issue of load allocation. A solution method that has been employed is offline scheduling based on a scenario that is scripted as a deterministic mathematical programming model.
If the society steers toward further energy saving, innumerable solar energy sources are expected to be connected to related-art power grids. With solar light energy which fluctuates depending on the goings-on in nature, the related-art method of running power houses by offline scheduling would not work well. This means that control needs to be capable of dealing with a very large number of control objects and dealing with an unexpected external disturbance. Offline scheduling cannot be used for dealing with an unexpected external disturbance, and a method of solving the unit commitment problem in real time for innumerable electric power nodes (on a large scale) will be sought after in the future. However, the unit commitment problem is very hard to solve in real time. Moreover, such a problem that how to treat a large number of control objects exists.
The unit commitment problem exists in the IT field as well. Examples of control exerted in a system of the IT field include load balancing among computer resources, network load balancing, and decentralized storage arrangement. The unit commitment problem is a problem observed in various fields, and a name of each control object which is activated or shut down, or on which a load is imposed includes various names such as function block, element, resource, and node depending on the fields. The control object is herein mainly referred to as “function block”, but it should be noted that a different name may be used depending on a context.
A description is now given of a related-art load balancing method while load balancing control for computer resources at a data center including a plurality of servers is used as an example. The basic idea of the related-art method eventuates in “balancing the internal state of the system”, which is rather unsophisticated. With this mindset, while the control policy is clear in the case of a uniform system (where the plurality of servers are identical servers), what index is to be the basis of balancing is not clear in a mixed-machine system where different types of machines are used.
For instance, while it is known that the CPU utilization ratios of the respective servers are to be balanced in the case of servers having the same performance, it is not obvious how to balance the CPU utilization ratios of servers that have different performance characteristics in a manner that reflects the servers' respective performance. A result obtained by the queueing theory, which is an index often used in related-art control, is an index based on the theory of probability, and tells nothing about what means to use in order to lead the system to a stochastically steady state.
What this means is that, although the system may eventually satisfy requirements to be fulfilled such as response and throughput, the system has no guarantees or limitations with regard to processes in the middle and the situation of resources that are ultimately used. In other words, the resultant control is merely for fulfilling the required performance irrespective of whether the system is in a very inefficient state in terms of energy.
Under such control, the inefficiency grows as the system increases in scale, and is expected to be a serious problem. Shutting down a server that is to be shut down and activating a server that is to be activated with accuracy is important here, too, and server load balancing can also be considered as a type of the unit commitment problem. The unit commitment problem is a problem also associated with many control problems such as storage arrangement control.
As a document disclosing an invention related to this invention, there is known Patent Document 1. In Patent Document 1, there is such a disclosure that, in an electric power system where a plurality of power generation devices are arranged in a distributed manner, each of the plurality of power generation devices autonomously controls an output of the power generation device itself based on local information acquired from the power generation device itself and a part of other power generation devices out of information on a supply/demand balance in the power generation system and power generation efficiencies of the plurality of power generation devices.